As a vet nurse I can tell you that the Bob Martins stuff is NOT the same as Frontline! The ingredient is licensed as VPS so pharmacy, vet or SQP can prescribe it. Its not off the shelf, it may have SOME of the ingredient in it but not enough to need VPS status so wont work (like ALL of their products!)- some BM products KILL animals!!! seen it many times over!
Frontline Combo is the same as Frontline, it just has an added insect growth regulator in it. So the eggs can't hatch so stops environmental problem (90% of flea life cycle in the environment!), so its not weaker.